Did not quite get your point. If blowsing=browsing, then you are trying to temporarily disable browsing when you are downloading something, while always having an option to re-enable browsing! Trust me, it is one of the weirdest things I have ever heard.

Here is an easy solution: Close your browser when you don't want to browse, and re-open it when you want. Use any downloader software to download files. I think it fulfills your given conditions.